Fuel burning and air heating apparatus



Dec. 25, 1956 D. J. CLARK L 2,775,238

' FUEL BURNING AND AIR HEATING APPARATUS Filed Jan. 29, 1955 3 Sheets-Sheet 1 INVENTORS.

0. J. CLARK AND MS. DECKER, BYMM JR.

Dec. 25, 1956 D. J. CLARK ET AL 2,775,238

FUEL BURNING AND AIR HEATING APPARATUS Filed Jan. 29, 1953 3 Sheets-Sheet 2 INVENTORS. D. L7. CLA RK AND ME. DECKER.

acu/tia Dec. 25, 1956 D. J. CLARK ET AL 2,775,238

FUEL BURNING AND AIR HEATING APPARATUS Filed Jan. 29, 1953 5 Sheets-Sheet I5 IN VEN TOR S.

ZZJCL/ RK AND M S. DECKER,

in a limited space.

2,775,238 FUEL BURNING AND AIR HEATING APPARATUS Donald J. Clark and Maurice S. Decker, Jr., Columbus, Ohio, assignors to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application January 29, 1953,Serial No. 334,002

3 Claims. (Cl. 126-116) This invention relates to combustion apparatus and is especially adapted for burning large quantities of fuel In the prior art, attempts to burn greater quantities of fuel in a given space have met with a limitation beyond which the flame blows itself out. This invention extends the limitation as to quantity of fuel which can be burned in given space limitations, providing a flame holder and many benefits as will presently appear.

For a consideration of what we believe to be novel and our invention, attention is directed to the following portion of this specification and the drawings and coneluding claims thereof.

In the drawings:

Fig. l showsan aircraft carried air heater embodying this invention. w

Fig. 2 is a longitudinal, partially sectioned view of the burner portion of the heater.

.Fig. 3 is. a longitudinal, sectional view of the central heat exchanger portion of the heater.

Fig. 4 is a longitudinal, sectional view of the discharge end portion of the heater.

Figs. 5, 6, 7, 8, and 9 are sectional views taken on lines 5-5, 6-6, 7-7 and 9-9 of Fig. 2 and line 8-8 of Fig. 3.

Fig. 10 is a longitudinal sectional view of a portion of the heater taken on line 10-10 of Fig. 5.

Fig. 11 is a longitudinal sectional view of a portion of the heater taken on line 11-11 of Fig. 7.

Fig. 12 is a partially sectioned longitudinalview of an alternate burner according to the invention.

Fig. 13 is an end view of the burner of Fig. 12.

Figs. 14 and 15 are sectional views .of the burner of Fig. 12 on lines 14-14 and 15-15 thereof.

The aircraft heater illustrated in Figures 1 through 11 is designed to use the propulsion fuel for the aircraft, such as gasoline, to produce heat by combustion and thus heat air for use in the aircraft for comfort heating, de-icing and the like. The heater comprises acasing 21 to which air is delivered at its inlet end 22 and from which heated air is delivered through its hot air outlet 23. Flue gas is exhausted from the exhaust gas outlet 24. Liquid fuel is delivered to the heater by a fuel supply conduit terminating in a nozzle 25 which is preferably of the spray type, but which is primarily a metering device for the fuel.

Air to be heated, or ventilating air, is delivered to the inlet end of the casing 21 by an air ram, a blower, or a bleed from a supercharger or the like, and may be, at a substantial pressure such as 18 p. s. i. A small stream of the air delivered to the inlet of the casing is passed through an orifice26 in the casing 21 into a combustion air manifold 27, and the balance of the air stream is divided between a central passage in conduit 31 through the heater and an annular passage between the casing 21 and a combustion tube 32. The central and annular air streams are joined before discharge from the heater through the hot air outlet 23.

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The combustion air supply is bled from the ventilating air at the air inlet into the combustion air manifold, where the pressure is considerably reduced after passing through the orifice 26. The manifold 27 serves as a plenum chamber to divide the combustion air into three portions leading each portion to one of three air inlet chambers formed in the combustion tube. Each of the air inlet chambers 33, 34 and 35 formed in the combustion tube 32 is connected to the air manifold 27 by an orifice 36, 37 and 38, and a spiral vane 41, 42 and 43 is provided in each inlet chamber to give the air a whirling motion, the intermediate air stream being directed to rotate in a direction opposite to the other two. The vanes need not be long to be effective for air direction, but the long spiral serves as a spacer to maintain the inner surfaces of open-ended cylindrical shells 44, 45, 46, having integral flanges securing the same to the combustion tube, aligned and spaced from the combustion tube 32. Shells 44, 45 and 46 are shown as cylindrical, but it seems clear that their circular shape is of primary importance, since some variation in longitudinal section from a straight line would affect cost of manufacture far more than operability.

A central tube 47 extends axially through the combustion tube 32 and is .joined therewith by a bellows 51 which forms an air tight expansion joint between the bellows 51 and an end plate 52 forming a part of the combustion tube 32. The central tube 47 extends through the heater to the vicinity of the hot air outlet 23 where it joins the side of the combustion tube to deliver the central air stream into the annular air stream, both of which streams then discharge through the hot air outlet. This discharge end of the central tube is joined to the combustion tube, and relative axial expansion between the tubes, due to operation at elevated temperatures, is accommodated by the bellows 51 which is maintained cool by the cool stream of air entering the heater. The central tube is also held spaced from the combustion tube along its length by spacer tabs 53. The central air tube performs several other useful functions as will appear, and the importance of its circular form will become apparent.

Air under pressure is delivered to the first air chamber 33 between the combustion tube inner surface 44 and its outer surface by the air manifold 27, the flow of air into that air chamber being controlled by a flow proportioning orifice 36. Fuel, preferably the liquid fuel which powers the aircraft, is injected into the air stream as it whirls (due to the vane 41) by a fuel injector nozzle 25 in the end of the fuel supply conduit. The fuel and air mixture so formed will generally be quite rich, for easy ignition and desiredrburning, and the mixture whirling in a clockwise direction looking downstream in chamber 33 of Figure 5, which becomes a counterclockwise direction in the combustion space travelling downstream of the heater. As the whirling mixture of fuel and air enters the combustion space it is ignited by a spark from a spark plug 55 which extends through the side of the heater into the combustion space. The upstream end of the central air tube serves as one electrode, a ground, for the spark plug, and ignition is thus effected towards the center of the whirling air stream where velocity is relatively low and where the rich fuelair mixture tends to cling to the central circular tube 47.

Air under pressure is delivered from the combustion air manifold 27 through the distributing orifice 37 into the second air chamber between the combustion tube 32 and the inner shell 45 where the helical vane causes the air stream to rotate in the second air chamber counter to the direction of rotation of the ignited fuel and t air mixture which is travelling downstream in the combustion chamber from the spark plug.

As the rotating stream of ignited fuel and air from the spark plug meets the counter-rotating air stream from the second air chamber, a zone of great turbulence is formed in which, due to rapid mixing and ventilation of the initially rich, ignited mixture by air, combustion is very greatly accelerated. This acceleration of combustion in the zone Where the counter-rotating streams meet provides a very stable flame over a wide range of rates of burning fuel, although as will be appreciated the flame will be extremely turbulent, or dynamic.

The stream of turbulent burning gases leaving the zone of great turbulence where the counter-rotating streams meet next adjacent the annular outlet from the second air chamber passes next adjacent the annular outlet of a third air chamber between the combustion tube 32 and the inner shell 46. Air is delivered to the third air chamber from the combustion air manifold l'l' through distributing orifice 38, and is caused to rotate therein in the same direction as the air rotating in the first air chamber, but counter to the direction of the air in the second air chamber. Thus a second zone of great turbulence is provided next adjacent the annular outlet from the third air chamber. Since this is the last air chamber for supplying combustion air to the burning fuel, it completes the delivery of the full complement of air for combustion of the fuel delivered to the first air chamber.

While it is preferred to deliver the fuel to the first air stream so that ignition may take place before the fuel enters the first zone of great turbulence, it is apparent that the fuel could alternatively be delivered to the second air chamber and ignited therein, or in certaincases to each of the chambers, especial y where the air is preheated either externally or by conduction of heat through the inner shells 44, 45 and 46 or by end wall 52. When fuel strikes these surfaces, it vaporizes rapidly and thus provides good mixing of fuel with air for ignition and combustion.

Axial flow air stream burners are very limited in the quantity of fuel which may be burned in a given space, especially where the chamber walls are not refractory. A simple whirling flame burner such as disclosed in patent to Trimble and Myler, .711, No. 2,445,341 greatly extended the quantity of fuel which could be burned at a given pressure without blow-off, and increased the al'titude range at which such a burner could satisfactorily operate. The present invention is another step forward in increasing the rate at which fuel can be burned, or the altitude at which the burner will operate, without blowotf.

In a burner according to this invention of about two inches diameter of combustion chamber, fuel was burned at a rate equivalent to the release of 14,000,000 B. t. u. per hour per cubic foot of combustion chamber, at a pressure of approximately 1 atmosphere, forming a flame hot enough to melt an lnconel red at over 2400 F. The metal tube 47 is thus placed in a zone of extreme heat, and melting of it is prevented only by passing a high velocity air stream through it. The central stream of air in the tube 47 absorbs about 30% of the heat which is transferred to the air while maintaining the central tube adequately cool. The inner surfaces 44, 45 and 46 of the combustion tube are likewise cooled to prevent burning or melting of the metal.

1 e central tube is abruptly expanded in size between the second and third air chamber outlets, or between the first and second zones of great turbulence, to further improve combustion, and further down stream it is again expanded in size to reduce the volume of the flue gas passage between the central tube 47 and the combustion tube 32, increasing velocity of the flue gases and thus irnproving heat transfer. A closed cylindrical plug 56 is disposed within the expanded portion of the central air tube 47 and spaced therefrom by tabs 57 to increase the velocity of air in that portion of the central air tube,

4 thus increasing heat transfer by convection. The plug 56 also absorbs heat by radiation from the tube 47 and transfers it by convection to the air tube 47, increasing greatly the convection heat transfer surface for heating the central air stream. Downstream of the cylindrical plug 56 the central air tube 47 contracts and is joined to the combustion tube 32 to discharge air into the annular air stream wherefrom the air leaves the heater through conduit 23.

The discharge end of the combustion tube 32 is slideably supported in an expansion seal joint 58 :0 provide for relative axial movement between the casing 21 and the combustion tube 32. The casing is fixed relative to the combustion tube at the burner end of the heater by the fuel inlet and spark plug assemblies.

A simplified burner design having no central tube and but a single dynamic flame holder is shown in Figures 12 through 15. This alternative design is shown as a burner only, not an air heater, to illustrate a burner adaptable for many purposes including generation of flue gases for inert atmosphere use or generation of hot combustion gases for gas turbines and the like. Modifled designs of this burner may be made to temper the temperature of the gases of. combustion to prepare them for use in a gas turbine.

The alternate burner comprises a combustion tube 61 having inner open-ended cylindrical shells 62 and 63 forming with the combustion tube annular air chambers. Air is delivered under pressure through conduit 64 and into the respective air chambers. Openings into the air chambers next adjacent the longitudinal dividing wall 65 but on opposite sides thereof cause the air in the re spective chambers to rotate in opposite directions.

Fuel is delivered by a fuel nozzle 66 to the first air chamber where it is vaporized by heat from the inner surface 62 before passing into the central combustion space. A spark plug 67 ignites the rich fuel and air mixture which enters the combustion space through the annular outlet from the first air chamber rotating at a high velocity. The fuel and air mixture adjacent the center tube, presumably due to frictional resistance to flow thereadjacent, fiows at a relatively low velocity in a film next adjacent the wall of the tube 47, thus forming a zone of stable combustion in the first whirling stream before the ignited rich mixture passes next adjacent the annular outlet from the second air chamber, where it meets the air therefrom which is rotating in the opposite directiom'thus forming a zone of high turbulence. This burner as shownis especially useful in producing completely burned fuel from stoichiometric or lean air-fuel mixtures, since rapid combustion takes place with no hot metal parts adjacent the combustion zone. The center tube 47 acts as a flame holder for stable combustion,

and the zones of great turbulence formed by the counterrotating streams serve to'complete the combustion in a very small volume without the aid of hot refractory parts or lining.

Modifications of the burner, such as axial admission of ventilating air for direct admixture with the flue gases, or admission of a third air chamber for delivering excess of air to dilute combustion gases, may be desirable in certain cases where the flame holder and complete combustion are desired, but lower maximum flue gas temperatures are also desired. Where hot line gases are to be generated, as for gas turbines and the like, it may be desirable to supply fuel with an excess of air to the first annular air chamber. The fuel will be ignited in the first air stream but not completely burned therein, and the mixing and rapid combustion effects will then serve to complete the, combustion. A closely held uniformity of flue gas composition is thus obtainable.

We claim:

1. Combustion apparatus for burning normally liquid fuel with air, which comprises: first Wall means forming a tubular duct for containing the combustion chamber,

said duct having a front end and a discharge end; a first cylindrical shell in said duct next adjacent said front end: annular end wall means join'ng the end of said shell toward said discharge end to said tubular duct; an aperture formed in the tubular duct adjacent said shell for delivering a first stream of air for combustion to the space between the duct and the shell; means disposed between the shell and the duct for causing air therein to whirl about the axis of the duct and to discharge substantially uniformly over the periphery of the sleeve towards the front end of the duct; a second cylindrical shell in said duct disposed towards said discharge end from said first shell; second annular wall means joining the end of said shell towards said discharge end to said duct; a second aperture formed in the tubular duct adjacent said second shell for delivering a second stream of air to the space between the second shell and said duct; means disposed between the second shell and the duct for causing air therein to whirl about the axis of the duct in a direction opposed to the direction of Whirl of the first stream of air and to dis charge substantially uniformly over the periphery of the second sleeve towards the front end of the duct; wall means for closing the front end of said tubular duct and comprising wall means forming a circular tube adjacent said front end and axially centered in said tubular duct; means for delivering normally liquid fuel to said first air stream whereby a rich mixture of fuel and air flows adjacent the circular tube at a relatively slow velocity as compared to the bulk of the fuel and air mixture stream, thus stabilizing combustion in said tubular duct; and means for igniting the mixture in said first stream in a manner to initiate combustion before said first stream meets said second stream.

2. Combustion apparatus for burning normally liquid fuel with air, which comprises: first wall means forming a tubular duct for containing the combustion chamber, said duct having a front end and a discharge end; a first circular shell in said duct next adjacent said front end; annular end wall means joining the end of said shell toward said discharge end to said tubular duct; an aperture formed in the tubular duct adjacent said shell for delivering a first stream of air for combustion to the space between the duct and the shell; means disposed between the shell and the duct for causing air therein to whirl about the axis of the duct and to discharge substantially uniformly over the periphery of the shell towards the front end of the duct; end wall means for closing the front end of said tubular duct and comprising wall means forming a circular, tube for a substantial distance from said front end and axially centered in said tubular duct; means for delivering normally liquid fuel to said first air stream whereby to form adjacent said tube a film of airfuel mixture which moves at a relatively slow velocity as compared to the bulk of the mixture, thus stabilizing combustion in said tubular duct; and means for passing a second air stream through said circular tube to cool the same. i

3. Apparatus according to claim 2 and comprising second wall means forming a second tubular duct surrounding said first mentioned tubular duct and forming therebetween an annular passage for air to b'eheated by the apparatus, said circular tube being connected to said first mentioned tubular duct adjacent said discharge end to discharge said second air stream into said annular passage.

References Cited in the file of this patent UNITED STATES PATENTS 

